406TPI

iTrader: (1)

Okay, someone help me understand what's going on here. It seems to me there are two seperate schools of thought on rear LCA's. You either have a super rigid boxed unit with poly bushings or you have the rod-end style which allow for almost an infinate amount of movement.

As far as the boxed/poly units go, it seems as though they would almost have a tendency to bind up the rear axle, ie. limit the amount that the axle can articulate around the the torque arm. Where as the rod end style would do the opposite. Which is better? Does it specifically depend on what you will be doing with the car, ie. drag racing vs. autocrossing? It almost seems as if the factory LCA's are a compromise?

I had my factory LCA's off the car the other day, with the steel stock all cut and ready to weld in to box them when all this noise came into my head....so I defer to the suspension experts here

RB83L69

Boxing stock arms improves them somewhat; but you're still stuck with a bunch of 15-year-old rubber bushings. Personally I wouldn't bother. Oh wait, not just "wouldn't", I didn't.

I have the Lakewood ones which are solid tubing (happens to square cross-section tubing) with poly bushings. Seem to work just fine. I think the hype about poly bushings "binding" the rear end is just that, hype; whilke I'm sure that on an autocross course or the like, the rod-end ones will beat the bushing ones every time, I can't see it making any difference on the street.

89 Iroc Z

The rod-ends are better but not practical for the street unless you want to replace the rod ends all the time and if you don’t mind the racket it will make. If your car is a street car and you want the best get some good chrome moly LCA’s with poly bushings like Spohns or BMR’s. If your car is only for track use then get fully adjustable rod-ends. Yes poly will bind but I think it is worth the ride quality over rod ends on a street car. I boxed my stock LCA’s because it was free but it is not going to give you much of any improvement.

Justins86bird

I dont know. I hated the poly/poly LCAs. Maybe that's because I was used to the rod/rod LCAs. rattle rattle . But its quiet with a poly/rod setup I'm running now, and handling is just as good on the street as with the rod/rod. Higher quailty rod ends will last longer then the cheapies. I went 4 years on the orig rod ends, been over a year now on the replacement and its still quiet.

I wouldn't bother boxing the LCAs.

406TPI

iTrader: (1)

Hey guys, thanks for the feedback! What I am really looking for is the theroy behind it all. If you break it down to the fundamentals, boxed with poly( ie, very rigid) or rodend (very un-rigid) you see they are complete opposite in their purpose but both claim to do the same thing?...ie, reduce wheelhop and improve traction over the factory units.

How is this possible?? Like I said before, it seems as though the factory units are a compromise between the two. They do allow flex but not near the amount of what a rod-end style unit would. Do you guys see what I am saying or am I not making any sense?

I guess the conclusion that I have come to is that the boxed/poly units are only good for straight line acceleraction period, while the rod-end units are more for improving the cars handling overall, especially when it comes to turning. The rod-ends take binding out of the equation so the suspension can be tuned more accurate and consistant.

Not that all this is really important, like I said, I just started thinking about all this the other day and it got me wondering. Is there something I missing or not taking into considration?

RB83L69

There is little or no difference on the street.

I can't figure out exactly what you're referring to as "box/poly". If you're talking about factory arms, boxed in with an extra piece of sheet metal with poly bushings installed, that's an awful lot of effort and expense to go through on such a piece of junk to begin with. That's what most people are talking about when they say "boxed" LCAs. If on the other hand you're talking about aftermarket ones made out of tubing, whether it be square cross-section tubing or round tubing (which there's no significant difference in, just a matter of the mfr's preference), then there's a slight advantage in all-out racing performance with the rod-end type. You typically see only round ones equipped with rod ends, because it's easier (less mfg steps) to screw rod ends into inside-threaded round tubing; but there's no reason you couldn't use square tubing and rod ends. It would just cost more to make and not be any better.

Again, IMHO, the difference in aftermarket LCAs between poly bushings and rod ends is not a concern on the street, regardless of the tubing cross section chosen by the maker.

Justins86bird

Maybe this thread will help you.
https://www.thirdgen.org/techbb2/sho...hreadid=237128

406TPI

iTrader: (1)

Justin, thanks for the link...I had started following that when it was first posted but forgot to follow up on it.....there is some really good info in there. Kinda goes along with what I was thinking.

RB....when I say boxed/poly I am mean any arm that has a round or square cross-section with poly bushings at both ends. You say that the factory arms are "junk" I'm not so sure that is true.

As I said before.....the factory arms appear to be a compromise between handling and straight line traction. If you are into drag racing, sure boxed units are the way to go, super rigid, reduces wheel hop by forcing both tires into the ground at the same time rather than alllowing them to "bounce" off one another. However, if you are more into a handling car, one that is predictable going in to and coming out of the corners, rod-end arms are more consistant as stated in the other post.

As for the bind issue....it is very clear (to me) that the boxed poly arms would cause alot of bind in the rear axle as it wants to rotate around the torque arm...this is what gives it the "reduced wheel-hop" characteristic. You reduce the bind or eliminate it with rod-end arms then you invite wheel-hop. You will then need to control wheel-hop by the valving in the shocks and the springs.

Am I off base or on the right track?

contactpatch

Keep in mind that the only purpose of the LCAs is
to transmit a longitudinal force (thrust) to the car.
Panhard handles side force.
Factory LCAs use rubber bushings for NVH,
but that, in effect, puts two rubber blocks
between the thrust (axle) and load (car).

MrDude_1

this is where you went off..


the axle moves in the arc the LCAs make... it does not move with the TQ arm, it moves with the LCAs.


the TQ arm DOES follow a diffrent arc, however, it has a slip fit in its bushing, so it can move in and out freely... thats how the TQ arm follows the LCAs arc without binding.



rod end LCAs are still extremely rigid. thats why they're used in all forms of motorsports for suspension. thats also why they're used here.
they arnt any less rigid. they will not go IN the arm or pull OUT.. that is the only force the LCA should take. it can freely move in all other directions. (bushings can also do the same thing. they DONT "bind"... and if you think they do, then you obviously havent messed with a LCA when half of it is bolted to somthing)

the upside to rod ended ones is that they allow adjustment.
the downside is service life... they eventually wear out.

the upside to poly bushing non adjustible ones is they last forever..
downside is they are not adjustible.



there are some out there that have the adjuster in the middle and poly at both ends. you get long life and adjustment that way...
but they are usually heavy, and if you dont tighten the jam nuts, the adjustment can change... with rod ends they're "trapped" somewhat.
then again, if you set them right, the locknuts wont come loose.

Dewey316

what the heck does the bushing type have to do with adjustment?

It all comes down to 2 factors

1) Bind

2) Deflection

Rod ends are better in BOTH areas, they have less deflection, and do not bind. it is a win/win for performance, the only downside is wear.

the compromise here, is a combo poly/bearing arm, with 1 bearing, you get rid of the binding, and only have 1 bearing per arm that will need to be replaced with the time comes, having 1 poly bushing on the body side attachment helps keep the noise down a little too.

MrDude_1

nothing other then most poly ones arnt adjustible.... the only adjustible poly LCAs i know of have the adjuster in the middle and i mentioned that at the end of my post.

406TPI

iTrader: (1)

Mrdude....No, I didn't go off. Maybe I'm just not explaining myself clearly. Every one here knows that the axle follows the arc set by the length of the LCA....however, the movement I am talking about is the rotation of the axle around the torque arm, or maybe I should say around the center section of the axle. Ie., if you are looking at a rear view of the car, it would be the movement of the left tire going up and the right tire going down or vice versa. This type of movement is what causes the factory LCA's to flex. The factory LCA's will not and cannot (within reason) flex in any other way. This type of flex (torsional)happens whenever the car enters, follows and leaves a turn. This is where I think everyone says that the the poly/boxed arms will bind causing unwanted and untunable action.

89 Iroc Z

Well if you have adjustable poly LCA’s the bind in the suspension has a tendency to cause the jam nuts to loosen and the LCA to fail or get out of adjustment. The rod end type don’t have this problem.

Justins86bird

You also have the arc created by the panhard bar (as the rear moves up and down, the axle moves left/right), not to mention the twisting effect as the body rolls in a corner or when 1 wheel goes through a pot hole.

Dewey316

Trust me, i am more aware of this than you know. IIRC i am the one who originaly posted that in the other thread. I thought that Senior Dude, was saying that benifit of a rod-ended LCA, was that you can get them adjustable. the bushing type really has nothing to do with the adjustment feature.